Technical Field
The present disclosure relates to a multi-sensor optical device for detecting chemical species, as well as to the manufacturing method thereof.
Description of the Related Art
As is known, in different fields of application one can detect one or more chemical species and then determine the corresponding concentrations of these chemical species. For instance, in the motor-industry sector, one can determine the concentrations, in an exhaust gas, of chemical species that are generated in the course of the thermal reactions that take place within an engine.
Once again with reference to the motor-industry sector, it is known that, following upon a combustion reaction that occurs between the fuel and the air, water (H2O), carbon dioxide (CO2), carbon monoxide (CO), sulphur oxides (SOx), nitrogen oxides (NOx), hydrocarbons (HC) and particulate matter (PM) are generated. In addition, nitrogen oxides include nitrogen monoxide (NO), nitrogen dioxide (NO2), and dinitrogen oxide (N2O).
Since the chemical species resulting from a combustion reaction concur significantly in pollution, the control of the levels of emission of these chemical species proves to be of particular importance. Consequently, various types of sensors have been developed over time, referred to in general as burnt-gas sensors. For instance, different types of nitrogen-oxide sensors are known, which are commonly employed within closed control loops that are designed to control the combustion process.
Since the aforementioned burnt-gas sensors usually operate in extreme environmental conditions, they are characterized not only by high sensitivity and speeds of response, but also by a considerable resistance to high temperatures, as well as to corrosive chemical agents. For this reason, known sensors are of silicon carbide (SiC), as described, for example, in the patent application no. DE20051033639. In this patent application a sensor is described including a sensing region of porous material, coated with a functional layer, capable of reacting with the chemical species to be analyzed; the reaction involves a detectable variation of the concentration of the carriers within the functional layer.
In general, burnt-gas sensors based upon the variation, following upon absorption of a chemical species by a constitutive element thereof, of an electrical characteristic of this element are characterized by low costs and by a certain simplicity of construction; however, they are likewise characterized by a not particularly high sensitivity, as well as, at times, by a low selectivity in regard to the chemical species absorbed. In addition, these sensors are far from suited to operating in the presence of corrosive chemical agents.
Commercial products are likewise known of the type described in the document available at http://www.baytec-inc.com/pdf/defor-extractive-analyzer.pdf. Illustrated in this document is a gas analyzer including a source of UV radiation and two optical detectors. Further, the analyzer enables detection of more than one chemical species, thanks to the use of a motor-driven mobile element, constrained to which is an optical filter so that the optical filter may be coupled to one of the optical detectors in a controlled way. Even though this system is characterized by a high accuracy, it may not be integrated; thus, it presents large overall dimensions and a high complexity. Consequently, this system is mainly suited for laboratory tests.